为flexdashboard gauge添加刻度标记并高亮颜色分界点

flexdashboard原生gauge函数不支持直接添加刻度标记，但可以通过自定义CSS或替换为更灵活的组件来实现需求，以下是两种可行方案：

方案1：自定义CSS强化分界+模拟刻度 #

步骤1：给仪表盘添加自定义ID #

在R代码中为仪表盘元素设置唯一ID，方便后续CSS定位：

flexdashboard::gauge(42, min = 0, max= 100, 
                     abbreviateDecimals = 2,
                     sectors = flexdashboard::gaugeSectors(success = c(0,50),
                                                           warning = c(50,75),
                                                           danger = c(75,100),
                                                           colors = c('green','yellow','red')),
                     .id = "custom-gauge")

步骤2：插入自定义CSS代码 #

在flexdashboard的YAML配置下方添加CSS，实现颜色分界高亮和模拟刻度：

---
title: "自定义仪表盘"
output: flexdashboard::flex_dashboard
---

<style>
/* 强化颜色区块的分界线条 */
#custom-gauge .gauge-segment {
  border-left: 2px solid #333 !important;
}

/* 添加刻度标记 */
#custom-gauge::before,
#custom-gauge::after,
#custom-gauge .gauge-segment:nth-child(2)::before {
  content: "";
  position: absolute;
  width: 4px;
  height: 15px;
  background: #333;
  top: -5px;
  z-index: 10;
}

/* 定位0、50、100刻度位置 */
#custom-gauge::before {left: calc(0% - 2px);}
#custom-gauge .gauge-segment:nth-child(2)::before {left: calc(50% - 2px);}
#custom-gauge::after {left: calc(100% - 2px);}

/* 添加刻度数值标签 */
#custom-gauge::before {content: "0"; height: auto; top: -25px; font-size: 12px; color: #333; width: auto;}
#custom-gauge .gauge-segment:nth-child(2)::before {content: "50"; height: auto; top: -25px; font-size: 12px; color: #333; width: auto;}
#custom-gauge::after {content: "100"; height: auto; top: -25px; font-size: 12px; color: #333; width: auto;}
</style>

### 仪表盘展示
```{r}
flexdashboard::gauge(42, min = 0, max= 100, 
                     abbreviateDecimals = 2,
                     sectors = flexdashboard::gaugeSectors(success = c(0,50),
                                                           warning = c(50,75),
                                                           danger = c(75,100),
                                                           colors = c('green','yellow','red')),
                     .id = "custom-gauge")

## 方案2：用plotly实现精准刻度与分界高亮
如果需要更专业的样式控制，推荐使用plotly的仪表盘组件，原生支持刻度配置和分界高亮：
```r
library(plotly)

plot_ly(
  type = "indicator",
  mode = "gauge+number",
  value = 42,
  gauge = list(
    axis = list(range = list(0, 100), tickvals = c(0,50,75,100), ticktext = c("0","50","75","100")),
    bar = list(color = "gray"),
    steps = list(
      list(range = c(0, 50), color = "green"),
      list(range = c(50, 75), color = "yellow"),
      list(range = c(75, 100), color = "red")
    ),
    threshold = list(
      line = list(color = "black", width = 4),
      thickness = 0.75,
      value = 75 # 高亮success到danger的分界点
    )
  )
)

内容的提问来源于stack exchange，提问作者Overtime4728