Refined control sizes.

src/components/MainPage.jsx

@@ -216,17 +216,21 @@ function MainPage({
           mb: 1,
           flexShrink: 0,
           bgcolor: "background.paper",
-          p: 1.25,
           border: 1,
           borderColor: "divider",
+          overflow: "hidden",
         }}
       >
         <Box
           sx={{
+            px: 2,
+            py: 1,
+            bgcolor: "action.hover",
+            borderBottom: 1,
+            borderColor: "divider",
             display: "flex",
             alignItems: "center",
             justifyContent: "space-between",
-            mb: 0.75,
           }}
         >
           <Box sx={{ display: "flex", alignItems: "center", gap: 1 }}>
@@ -236,25 +240,27 @@ function MainPage({
             </Typography>
           </Box>
         </Box>
-        <TextField
-          fullWidth
-          size="small"
-          placeholder="Enter JMESPath expression (e.g., people[*].name)"
-          value={jmespathExpression}
-          onChange={handleJmespathChange}
-          error={!!error}
-          helperText={error || " "}
-          sx={{
-            "& .MuiInputBase-root": {
-              fontFamily: "'Noto Sans Mono', monospace",
-              fontSize: "0.9rem",
-            },
-            "& .MuiFormHelperText-root": {
-              mt: 0.75,
-              mb: -0.5,
-            },
-          }}
-        />
+        <Box sx={{ p: 1.5 }}>
+          <TextField
+            fullWidth
+            size="small"
+            placeholder="Enter JMESPath expression (e.g., people[*].name)"
+            value={jmespathExpression}
+            onChange={handleJmespathChange}
+            error={!!error}
+            helperText={error || " "}
+            sx={{
+              "& .MuiInputBase-root": {
+                fontFamily: "'Noto Sans Mono', monospace",
+                fontSize: "0.9rem",
+              },
+              "& .MuiFormHelperText-root": {
+                mt: 0.75,
+                mb: -0.5,
+              },
+            }}
+          />
+        </Box>
       </Paper>
 
       <Grid container spacing={3} sx={{ flex: "1 1 0", minHeight: 0, height: 0 }}>